In recent years, low heat buildup property has been strongly sought for automobile tires due to environmental issues and resource issues. Furthermore, from the viewpoint of safety, excellent wet grip and strength are demanded. A tire obtained using a rubber composition containing silica as a filler is better in low heat buildup property compared with a tire obtained using the conventionally used rubber composition including carbon black, so it is possible to produce tires more excellent in low fuel consumption.
As a conjugated diene rubber used for giving such a low fuel consumption tire, Patent Document 1 discloses a conjugated diene rubber obtained by reacting a specific tin halide compound with a conjugated diene polymer chain having an isoprene block at one end and an active end at the other end. Further, Patent Document 2 discloses a conjugated diene rubber containing a certain amount or more of a structure comprised of three or more conjugated diene polymer chains bonded together obtained by reacting a specific modifying agent with a conjugated diene polymer chain having an isoprene block at one end and an active end at the other end.